Method and system for on-line monitoring of bearing insulation in an electrical generator

Abstract

The present invention monitors an electrical generator ( 10 ) to provide an indication of a problem in the generator's bearing insulation ( 26 ), such as insulation damage or insulation bridging, and sets an alarm to warn an operator of the problem, thereby avoiding damage to the electrical generator ( 10 ). Methods and systems consistent with the present invention identify problems with bearing insulation ( 26 ) by monitoring the naturally occurring shaft voltage on the generator rotor ( 12 ) and by setting an alarm if the shaft voltage drops below a predetermined value.

What is claimed is:  
     
       1. A method of identifying a problem with bearing insulation in an electrical generator, comprising the steps of: 
       monitoring shaft voltage over the length of a rotor of the electrical generator; and  
       setting an alarm, when the shaft voltage drops below a predetermined value, to provide an indication of the bearing insulation problem to an operator;  
       wherein the step of monitoring shaft voltage includes mounting at least one shaft-riding brush to the rotor to provide an indication of the shaft voltage to a data-processing system; and  
       wherein the step of setting an alarm includes tripping the electrical generator.  
     
     
       2. The method of  claim 1  wherein the predetermined value is about 5 bolts. 
     
     
       3. A monitoring system for identifying a problem with bearing insulation in an electrical generator, comprising: 
       means for monitoring shaft voltage over the length of a rotor of the electrical generator;  
       means for setting an alarm, when the shaft voltage drops below about a predetermined value, to provide an indication of the bearing insulation problem to an operator;  
       a data-processing system and at least one shaft-riding brush mounted to the rotor of the electrical generator for providing an indication of the shaft voltage to the data-processing system; and  
       a relay for tripping the electrical generator when the shaft voltage drops below the predetermined value.  
     
     
       4. The monitoring system of  claim 3  wherein the predetermined value is about 5 volts. 
     
     
       5. A monitoring system for identifying a problem with bearing insulation in an electrical generator, comprising: 
       at least one shaft riding brush mounted to a rotor of the electrical generator for providing an indication of a shaft voltage across the electrical generator;  
       a data-processing system for monitoring the shaft voltage and for setting an alarm when the shaft voltage drops below a predetermined value to provide an indication of the bearing insulation problem to an operator; and  
       a relay for tripping the electrical generator when the shaft voltage drops below the predetermined value.  
     
     
       6. The monitoring system of  claim 5  wherein the predetermined value is about 5 volts.